Intramedullary, flexible fracture fixation device, using bi-axial prestressing

ABSTRACT

The invention refers to a prosthetic device for the application of simultaneous axial and transversal prestressing to obtain stable and elastic osteosynthesis of fractures. The device focuses on the concept of internal fixation with consideration for the natural frequency of the bone. The device for fracture fixation comprises a “tendon” (i.e, a tensionable wire) least one deformable element at the focus of the fracture, with the tendon and the deformable element being disposed almost parallel, whereby the device further comprises compression means to apply a compression force to the deformable element(s), so that the deformable element(s) deform(s) laterally. The device described can be used for fractures of long bones as well as for proximal femoral fractures. When used for long bone fractures, the device is an intramedullar flexible bar, with which we apply adjustable and measurable axial prestressing in order to compress the bone fragments and preload the bone. When used for proximal femoral fractures, the device is the same intramedullar flexible bar, with which we apply adjustable and measuring lateral prestressing while anchoring it on the femoral shaft exterior. By doing so we compress the bone fragments in order to neutralize the tension forces on the fracture and to avoid interfragmentary motions. The terms “axial prestressing” and “lateral prestressing” refer to axis long bone. The device allows us to achieve predetermined and measurable intramedullar transversal prestressing, which is a prerequisite for the application of axial prestressing.

BACKGROUND OF THE INVENTION

The invention refers to a device for fracture fixation. Devices forfracture fixation are known from EP 0 698 800, which discloses affixingan elongated rod on the bone. Further, documents GB 2 268 068 and DE 923085 disclose devices for fracture fixation comprising at least adeformable element and compression means to apply a compression force tothe deformable element, so the deformable element deforms laterally.

Each of the well established fixation methods (rigid compressionplanting, reamed intramedullary nailing, with or without interlocking ofthe fracture fragments, external fixation and dynamic hip screw) hasadvantages and disadvantages as well as special biomechanicalcharacteristics. Vast clinical experience combined with the dataproduced from theoretical and experimental studies have described manyof the problems related to the biomechanics of these fracture fixationdevices.

Today's understanding of bone biology has led us to a new approach tobone fixation. This approach considers the importance of thepreservation of the soft tissue and of careful protection of theviability of bone. This invention aims to add to the theory and practiceof bone fixation the concept that the fracture fixation deviceintroduces into the broken bone equilibrium tensions to restore theintraosseous forces and make the bone capable of receiving the loadstresses and muscle-spasm stresses right at the beginning of the healingperiod, as opposed to the prior concept that it is the device thatreceives these stresses.

A first attempt towards these goals is disclosed by Protogirou in PCTInternational Publication Number WO 91/19461 (title: Device forOsteosynthesis with Axially Guided Prestressing Elements). This devicewas also trying to solve some of the problems related to thebiomechanics of bone fixation using axial prestressing to achieve stableand elastic osteosynthesis thus restoring the intraosseous forces. Theresetting of the fragments remains stable by the medullary guide and theaxial prestressing is applied through the tendons.

SUMMARY OF THE INVENTION

According to the invention the device for fracture fixation comprises, atendon and at least a deformable element at the focus of the fracture,whereby the deformable elements may be 2, 3, 4, 5, or more, with thetendon and the deformable element being disposed almost along the samedirection, whereby the device further comprises compression means toapply a compression force to the deformable elements, so that thedeformable elements deforms laterally. The device described can be usedfor fractures of long bones as well as for proximal femoral fractures.When used for long bone fractures, the device is an intramedullarflexible bar, by which is applied adjustable and readable axialprestressing in order to compress the bone fragments and preload thebone, and not a supportive intramedullar nail as the devices used sofarfor fracture fixation. When used for proximal femoral fractures, thedevice is the same intramedullar flexible bar, by which is appliedadjustable and readable lateral prestressing when anchoring it on theexternal femoral shaft. By doing so the bone fragments are compressed inorder to neutralize the tension forces on the fracture and to avoid theinterfragments motions. The terms “axial prestressing” and “lateralprestressing” refer to the axis of the long bone.

With the prosthetic device of the invention it is possible to applysimultaneously axial and transversal pre-stressing to pre-load the boneand obtain stable and elastic osteosynthesis of fractures. The devicefocuses on the concept of biological internal fixation with minimaldamage and with consideration for the natural frequency of the bone.

The device according to the invention presents a different approach tothe problem of fracture fixation in that it allows achievement ofpredetermined and readable intramedullar transversal prestressing, whichis a prerequisite for the application either of axial prestressing or oflateral prestressing. The transversal prestressing holds in place therepositioned bone fragments and contributes to the neutralization of thebending moments and the shearing forces between the fracture angle andthe mechanical axis of the bone caused by the axial prestressing in thecase of long bone fractures. In the case of proximal femoral fracturesthe transversal prestressing diminishes the interfragmentary motions.The term “transversal prestressing” refers to the “axial prestressing”and the “lateral prestressing” and is vertical to them.

Moreover, because the transversal prestressing can diminish the bendingmoments and the shearing forces caused by muscular spasm, the samedevice can be used as bone distractor for unstable long bone fractures.

The ability to compress the bone ends uniformly, In the case of longbone fractures, can be achieved through intramnedullary axialprestressing. But the fractured bone cannot receive compression forcesif it is not repositioned in a stable way, because of bending andshearing forces occurring as a result of compression. The resetting ofthe fragments remains stable and allows for the application of axialprestressing because of the prior application of intramedullarytransversal prestressing. In order to achieve this bi-axial prestressinga tendon is inserted intremedullarly and anchored in the one end of thebone. The tendon is passing through cylindrical bodies, which fit intoone another and form a flexible bar. At least one pair of cylindricalbodies bear attachment means for deformable elements. By applyingcompression to the cylinders by the compression nut the cylinders webrought together and compress the deformable elements, which deformlaterally and exercise pressure on the inner wall of the bone(transversal prestressing). As the tendon is already anchored in the oneend of the bone, tension is exercised on the tendon by a screw bolt withsupport on an anchor means, which is anchored into the other end of thebone (axial prestressing). In spite of the application of tension, theflexible bar does not become a straight bar, but on the contrary itfollows all the curvatures of the bone.

The neutralization of tension forces on the fractured proximal femoralbone can be achieved through lateral prestressing (tension band). Theapplication of lateral prerstressing becomes more efficient if theinterfragmentary motions are diminished. This is achieved by the priorapplication of transversal prestressing. In order to achieve this doubleprestressing an anchor screw is anchored in the head of the femur. Theother end of this anchor screw is formed as a cylinder with attachmentmeans at both its ends for the deformable elements. By applyingcompression to a compression means at the end of the cylinder other thanthe end bearing the screw, the deformable elements are compressed, whichdeform laterally and exercise pressure on the inner wall of the bone(transversal prestressing). The one end of the tendon is anchored at theend of the cylinder other than the end bearing the screw. The tendon isanchored by a ball means in order to form an articulation at this pointand thus diminish the motion between implant and bone. The tendon bendson the lateral femoral shaft with support on a fulcrum attached on aplate, which plate is screwed in the lateral femoral shaft. The otherend of the tendon passes through a cylinder fixed to the plate. Tensionis exercised on this end of the tendon with support on the cylinderfixed to the plate and the tendon is then anchored on the plate (lateralprestressing). In some cases of unstable fractures a second tension band(wire) is added to the above described device ends of the wire areintroduced in the form of a slip knot into the bone from the openingmade for the anchor means 2 b, towards the base of the femoral neck. Theslip knot is then anchored on the anchor screw, tightened over thegreater trochanter, and both its ends then anchored on the plate.

The following advantages can be observed compared with the previousfixation methods (rigid compression plating, reamed intramedullarynailing with or without interlocking of the fragments, external fixationand dynamic hip screw):

The resetting of the fragments is supported by the transversalprestressing.

One does not have to operate at the fracture area because the device isinserted intramedullary by the same technique as any intramedullary nailin the cases of long bone fractures, and it is inserted from the lateralfemoral shaft by the same technique as the present devices in the casesof proximal femur fractures.

The device is introduced without any reaming, and fills up theintramedullar area, thus allowing for early bearing.

The device is inserted easily and it does not affect the shape of thebone because it is flexible and self guided and follows the curves ofthe bone.

Friction between device and bone is minimal because of small and firmcontact between them.

The infection possibility and other complications are minimised.

The time of medical attendance and recovery is minimised.

The removal of the device is very easy.

Moreover, because the transversal prestressing can neutralism thebending moments and the shearing forces caused by muscular spasm, thesame device can be used as bone distractor for unstable fractures.

The possible mistakes are very few because the method is easy to learnand apply.

The use of x-rays is not necessary in many cases, and whenindispensable, the time of use is minimized.

The device does not affect the E-modulus and the blood circulation ofthe bone.

it is possible to assemble Individual device components of differentlengths, so as to achieve adjustment according to the geometry of thespecific bone (Universal and Modular).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood with the followingdetailed description of an embodiment for each type of fracture, longbone and proximal femur fracture, in connection with the accompanyingdrawings:

FIG. 1 is a representation of the device implanted into a femur bone.

FIG. 2 is a representation of the bolt 11.

FIG. 3 is a representation of the anchor means 12.

FIG. 4 is a representation of the nut 10.

FIG. 5 is a representation of the tendon 1 with anchor means 2 at itsone end and screw means 2 a at its other end.

FIG. 6 is a representation of torque means 5.

FIG. 7 is a representation of a cylindrical element 3.

FIG. 8 is a representation of the two cylindrical elements 6 and 7, andof the deformable element 9.

FIG. 9 is a representation of the device implanted into a proximal femurbone.

FIG. 10 is a representation of the anchor means 2 b.

FIG. 11 is a representation of a bolt 18.

FIG. 12 is a representation of the end of the tendon 1 b, which end isformed as a ball.

FIG. 13 is a representation of the deformable elements 9 b attached tothe attachment means 8 b.

FIG. 14 is a representation of the plate 14 with the cylinder 16.

FIG. 15 is a representation of the protrusion 15S, which is attached tothe head of the plate 14.

FIG. 16 is a section of the plate 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings the following detailed description of twoembodiments, one for a long bone fracture and one for a proximal femurfracture will help understand how we apply the above mentioned principleof bi-axial prestressing.

The tendon 1 for the application of axial prestressing can be awire-cable. Its one end is incorporated into an anchor means 2, whichmay be a self-taping screw, suitable for spongy bone. The head of theanchor means is cylindrical with two slots 4, dividing the perimeter ofthe cylinder into two protrusions which fit into the two slots of thepreceding cylindrical body 3. The other end of the tendon isincorporated into a screw means 2 a, for example a threaded bar.

The tendon is passing through cylinders. We have three kinds ofcylinders depending on their position on the device and their use. Allthe cylinders except the last one 5 towards the end of the device nearthe body have two opposite facing slots 4 at both their ends, dividingthe perimeter of the cylinder into two protrusions which fit into thetwo slots of the nearby cylinder, so as to allow the cylinders first tofit into one another and form a flexible bar, and second to transmit thetorsion force which we apply on the torque means 5 to the anchor means2.

The two cylinders 6, 7, which correspond to the focus of the fracture,have an overdrawn perimeter for part of their length, to provide placefor attachment means 8, in which the deformable laminated springs 9 areadapted. The length of the slots of these two cylinders on the end wherethey fit into one another is longer, so as to allow them to come closer,compress the laminated springs and let them bow and exerciseintramedullary pressure.

The torque means 5, placed last towards the end of the device near thebody is of similar shape to the cylinders 3 along half of its length.The other half of its length, towards the end of the device, has theshape of a screw nut as regards its external shape. A nut screwdriver isadapted to this half of the torque means 5 to screw the anchor means 2,by screwing the whole device around itself. The internal cylindricalopening of the part of the torque means 5 which fits Into the cylinder 3is of the same diameter as the openings of all the other cylinders so asto allow the tendon to pass through, whereas the part of the internalopening towards the end of the device is larger to let the threaded bar2 a adapted to the tendon fit into it and be stopped there so as to holdall the cylinders together.

A nut 10 is screwed around the threaded bar 2 a to bring all thecylindrical bodies 3,6,7 and torque means 5 together and compresslaminated springs 9, which by deforming laterally, exerciseintramedullar pressure, i.e. transversal prestressing.

The bolt 11 is then screwed around the bar 2 a after the nut 10, toapply tension to the tendon 1 with support on the anchor means 12 and onthe bone, thus exercising axial prestressing, that is preloading of thebone.

Bolt 11 may be replaced by an element with grooves on its outer side. Inthe case of such an element when screwed inside the anchor means 12 andby compressing the bar 2 a, it applies compression forces to the device,thus distracting the bone fragments when necessary.

The tendon 1 b for the application of lateral prestressing can be a wirecable. Its one end may have the form of a ball which is attached to abolt 18, which bolt is screwed around torque means 5 b. Torque means 5 bis actually the one end of an anchor means 2 b, and serves to screw theanchor means into the bone. The other end of the anchor means 2 b may bea self-taping screw, suitable for spongy bone. The body of the anchormeans 2 b is hollow because the anchor means is positioned with the helpof a drill guide. Around the cylindrical part of anchor means 2 bdeformable elements 9 b are disposed almost along the same direction,which are fixed at both their ends into attachment means 8 b. Beforescrewing bolt 18 around the one end of anchor means 2 b, we screw a nut10 b, which compresses the attachment means 8 b between eachother, thusdeforming the deformable elements 9 b laterally. The deformable elements9 b fill up the Ward's Triangle and exercise pressure on the inner sideof the bone (transversal prestressing).

A plate 14 is fixed with screws on the lateral cortex of the femur. Thisplate differs from the usual ones in two points. First it has aprotrusion 15 on its head, which serves as a fulcrum for the tendon 1 bto have a smooth change of direction of the tendon. Second, there is acylinder 16 fixed on the plate's body. The tendon 1 b is passing throughthis cylinder.

We exercise tension (lateral prestressing) on the tendon along its axis,with support against the cylinder 16. This tension may be easilymeasured and adjusted according to the necessities of the direction ofthe fracture, the weight of the patient and the form, dimensions andquality of the bone. This tension can be applied by means of adynanmmetric tensioner, which in this case plays the role of a tensionmeans. We then anchor the tendon on the plate with a securing means 17.This securing means 17 may be in the form of a deformable metal dip orcylinder, which can be deformed and pressed on the tendon In a fixedrelationship.

What is claimed is:
 1. A device for flexible fixation of long bone orproximal femoral fractures, said device comprising an elongatemechanical tendon adapted to apply axial prestressing or lateralprestressing to a fractured bone during fixation under tension inintramedullary position therein, said tendon having first and secondends with anchor means at the first end of said tendon and screw meansat the second end of said tendon, a plurality of deformable elementsheld captive between said first and second ends and generally disposedabout and along and substantially co-axial with the same longitudinalaxis as said tendon and adapted to be positioned at the focus of thefracture when said tendon is in said intramedullary position forfixation, compression components for adjustably applying a compressiveforce to said deformable elements to cause lateral deformation thereofrelative to said longitudinal axis adapted to transversely prestress thefractured bone at said focus, tension-applying elements comprising saidanchor means and said screw means adapted to apply tension force to saidtendon when in said intramedullary position for axial or lateralprestressing and fixation of the fractured bone simultaneous with saidtransverse prestressing, a plurality of cylindrical elements disposedabout said tendon with attachment means spaced apart on two of saidcylindrical elements for attaching the ends of said plurality ofdeformable elements thereto, said compression components being adaptedto be screwed on said screw means whereby to bring said two cylindricalelements together to compress said deformable elements and deform themlaterally, and thereby exercise intramedullary pressure transverseprestressing of the fractured bone.
 2. The device of claim 1, whereinsaid compression components include means for applying torque to saidanchor means for screwing said tendon onto the anchor means.
 3. Thedevice of claim 1, wherein said attachment means are slidable forretaining both ends of said deformable elements relative to said tendon,said attachment means coating with said compression components for saidcompression of said deformable elements and said lateral deformationthereof to a desired extent to enable distraction of bone fragments. 4.The device of claim 1, comprising bolt means and second anchor means atsaid second end of said tendon, said bolt means and second anchor meanscooperating with said screw means at said second end to apply a tensionforce to said tendon.
 5. The device of claim 4, comprising third anchormeans and securing means at said second end of said tendon and co-actingto maintain said tension force applied to said tendon.
 6. The device ofclaim 1, wherein said cylindrical elements have end slots to enablemating of adjacent ones of said cylindrical elements on said tendon andthereby form a flexible bar.
 7. The device of claim 6, wherein said endslots of at least two adjacent ones of said cylindrical elements areshaped to enable said at least two cylindrical elements to be broughtcloser together for compression of said deformable elements.
 8. Thedevice of claim 6, wherein the first-mentioned anchor means has aslotted cylindrical head adapted to mate with the end slots of theadjacent one of said cylindrical elements.
 9. The device of claim 1,wherein said tension-applying elements further include a bolt adapted tobe screwed onto an end of said anchoring element, and wherein said firstend of said tendon has the shape of a ball adapted to mate with a socketwithin said bolt.
 10. The device of claim 5, wherein said third anchormeans comprises a plate and a cylinder, said cylinder being attached tosaid plate.
 11. The device of claim 10, wherein said plate includes aprotrusion constituting a fulcrum for said tendon.
 12. The device ofclaim 1, including a biocompatible plate covering the entirety of thesurface of said device outside the fractured bone to provide a smoothexternal surface thereof.